Self-cleaning corona generating apparatus



Feb. 17, 1970 DQBQJUGLE 3,496,352

' SELF-CLEANING CORONA GENERATING APPARATUS Filed June 5, 1967 2Sheets-Sheet 1 CONTROL f LOGIC 1 5 mvrsmorz.v

DON B. JUGLE BY MMA.

Feb. 17, 1970- o 8. Juan; 3,496,352

SELF-CLEANING CORONA GENERATING APPARATUS Filed June 5, 1967 2Sheets-Sheet 2 I I78) fit in [057 g HIGH r CONTROL LOGIC -/5o INVENTOR.DON B. JUGLE M TOR/V5 rs United States Patent O 3,496,352 SELF-CLEANINGCORONA GENERATING APPARATUS Don B. Jugle, Penfield, N.Y., assignor toXerox Corporation, Rochester, N.Y., a corporation of New York Filed June5, 1967, Ser. No. 643,548 Int. Cl. H01j 37/26; G03g US. Cl. 25049.5 6Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Thisinvention relates to xerography and particularly to improved coronagenerating apparatus for applying an electrostatic charge onto arecipient surface.

In the process of xerography, for example, as disclosed in CarlsonPatent 2,297,691, issued Oct. 6, 1942, a xerographic plate comprising alayer of photoconductive insulating material on a conductive backing isgiven a uniform electric charge over its surface and is then exposed tothe subject matter to be reproduced, usually by conventional projectiontechniques. This exposure discharges the plate area in accordance withtheradiation intensity that reaches them, and thereby creates anelectrostatic latent image on or in the photoconductive layer.Development of the latent image is effected with an electrostaticallycharged, finely divided material such as an electroscopic powder that isbrought into surface contact with the photoconductive layer and is heldthereon electrostatically in a pattern corresponding to theelectrostatic latent image. Thereafter, the developed xerographic powderimage is usually transferred to a support surface to which it may befixed by any suitable means.

In automatic xerographic equipment, it is common to employ a xerographicplate in the form of a cylindrical drum which is continuously rotatedthrough a cycle of sequential operations including charging, exposure,developing and transfer. During the cycle, copy is reproduced onto asupport surface and after transfer, the plate is cleaned before reuse.It is usual to charge the xerographic plate with corona of positivepolarity by means of a corona generating device having an electrodewhich when supplied with potential above the corona threshold producesan emission corona ions that deposit uniformly onto the plate surface.Typical of the corona generating devices employed heretofore are thosedescribed in US. Patent 2,777,957 to Walkup and U.S. Patent 2,836,7 toVyverberg, each constructed generally of an electrode wire or wiressupported relatively close to the surface to be charged. A groundedmetallic shield generally surrounds the electrode except for an openingthrough which charge is emitted and is adapted to attract surplusemission emanating therefrom.

Inherent in xerographic apparatus of the type described above is thecontinuous presence of dust generated by the operations and generallycomprising particulate quantities of stray electroscopic powder. Withcontinuous operation, dust accumulates on and about the interior of thecorona generating device to such an extent that the charging efliciencythereof decreases substantially as the density of dust accumulationincreases. As a result there is a sharp drop-off in the quality ofprints reproduced.

To ensure a high charging efficiency the corona generating devicerequires frequent cleaning and maintenance. For example, in order tomaintain the entire apparatus operating effectively it has beennecessary to clean the corona generating device completely afterapproximately several hundred reproductions and even sooner withmachines operating at very high rates. Normally this necessitatesremoving the corona generating device from the machine and cleaning theentire assembly including wire and housing with a suitable cleaningsolution. It goes without saying that this is a very time consumingoperation not to mention the fact that the machine must remain idleduring this period and thus can be of no benefit to the user.

With millions of copies being printed yearly, the costs of servicingrepresents a significant economic overhead. At the same time in order toensure uninterrupted operation within a plausible programmed maintenanceschedule, it has been found necessary to operate these corona generatingdevices at a potential substantially above the threshold potential tomaintain the required potentail for corona emissions. When it isconsidered that many copying machines have several corona generatingdevices, the problem of how to clean the devices without adverselyeffecting machine operation or requiring machine shutdown becomesincreasingly apparent.

Now in accordance with the instant invention, there has been discovereda novel corona generating apparatus that is self-cleaning as to becapable of operating more elficiently than those used heretofore.Generally speaking the self-cleaning operation is accomplished byselectively flowing an electrical current through the generating deviceto raise it to a temperature sufiicient to vaporize and therefore cleanaway dust or stray electroscopic powder. In a second embodiment currentis also selectively flowed through -a portion of the housing adjacentthe generating device to efifect a combined cleaning action resulting ina more eflicient dissemination of corona discharge on the xerographicsurface.

SUMMARY OF THE INVENTION It is therefore an object of the invention toimprove corona generating devices for applying electrostatic charge ontoa recipient surface.

It is another object of the invention to enhance performance andincrease the operating efiiciency of corona generating devices whereby asubstantially greater proportion of total current is utilizedeffectively in applying charge onto a recipient surface.

It is a further object of the invention to provide a corona generatingdevice which is self-cleaning resulting in a prolonged consistency ofcharging efficiency.

It is a still further object of the invention to operate automaticxerographic equipment more economically than heretofore.

BRIEF DESCRIPTION OF THE DRAWINGS Further objects and features of theinvention will become apparent on reading the following description inconnection with the drawings wherein:

FIG. 1 is a schematic illustration of an automatic xerographic apparatusfor use with the corona generating apparatus of the invention;

FIG. 2 is a side view of the corona generating device and circuitryaccording to the present invention;

FIG. 3 is a partial plan view of one end of the corona generating deviceof FIG. 2;

FIG. 4 is a sectional view taken substantially along the line 44 of FIG.2;

FIG. 5 is a sectional view similar to that shown in FIG. 4 of a secondembodiment of the corona generating device, and

FIG. 6 is an electrical circuit for use with the corona generatingdevice shown in FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a general understanding ofthe Xerographic processing system in which the invention isincorporated, reference is bad to FIG. 1 in which the various systemcomponents are schematically illustrated. As in all xerographic systemsbased on the concept disclosed in the above-cited Carlson patent, aradiation light image of copy to be reproduced is projected onto thesensitized surface of a Xerographic plate to form electrostatic imagethereon. Thereafter, the latent image is usually developed with anoppositely charged developing material to form a Xerographic powderimage corresponding to the latent image on the plate surface. The powderimage is then electrostatically transferred to a support surface towhich it may be fused by any suitable form of fusing device, whereby thepowder image is caused permanently to adhere to the support surface.

The Xerographic apparatus described herein typically may be of the typedescribed in Cerasani et al. US. Patent 3,076,392. In the apparatusreferred to, copies to be reproduced, which usually are positive inform, are placed on a support tray 10 from which they are fed onto asuitable transport mechanism designated 11. Suitable drive means areprovided for the transport mechanism from motor 12 to endless belts 13whereby the copy is moved past the optical axis of projection system 14and illuminated by projection lamp LMP-l. The image of the copy isreflected by mirror 15 through an objective lens 16 and then isreflected by mirror 17 downwardly through a variable slit apertureassembly 18 and onto the surface of the Xerographic plate in the form ofdrum 19*.

Xerographic drum 19 includes a cylindrical member mounted in suitablebearings in the frame of the machine and is driven in a clockwisedirection by a motor 24 at a constant rate that is proportional to thetransport rate of the copy whereby the peripheral rate of the drumsurface is identical to the rate of movement of the reflected lightimage. The drum surface comprises a layer of photoconductive material 25such as vitreous selenium, on a conductive backing 26 such as aluminum.The photoconductive material is sensitized prior to exposure by means ofa self-cleaning corona generating device 30 as will be described morefully below, and which is energized from a suitable high voltage source31 (FIG. 2).

Exposure of the drum to the light image discharges the photoconductivelayer in the areas struck by light, whereby there remains on the drum alatent electrostatic image in image configuration corresponding to thelight image projected from the copy. As the drum surface continues itsmovement, the electrostatic latent image passes through a developingstation 35 at which a two-component developing material 36, which may beof the type disclosed in Walkup Patent US. 2,638,416, is cascaded overthe drum surface by means of developing apparatus 37. In the developingapparatus, developing material is carried upward by conveyor 39 drivenby suitable drive means from motor 40 and is released onto chute 41wherefrom it is cascaded down over the drum surface. Toner component 42of the developer, which is consumed in developing, is stored indispenser 43 and is released in amounts controlled by gate 44.

After developing, the Xerographic powder image passes a dischargestation 50 at which the drum surface is illuminated by a lamp LMP-Z,whereby residual charges on the non-image areas of the drum surface arecompletely discharged. Thereafter, the powder image passes through animage transfer station 51 at which the powder image is electrostaticallytransferred to a support surface web 52 by means of a second coronagenerating device 53 similar to corona generator 30 as will behereinafter described.

The support surface to which the powder image is transferred may be ofany convenient type such as paper and is obtained from a supply roll 54to pass over guide rolls 55 and 56 and over suitable tensioning rollsbeing directed into surface contact with the drum in the immediatevicinity of transfer corona generating device 53. After transfer, thesupport surface is separated from the drum and is guided through asuitable heat fusing apparatus 57 whereby the powder image ispermanently affixed to the support surface. Thereafter, the supportsurface is fed over a further system of guide and tensioning rolls andonto a take-up roll 58 that is driven by motor 59.

Following separation of the support surface from the drum, a coronagenerating device 65, likewise constructed in accordance with theinvention hereof as will be further described below, directs negativeelectrostatic charge to the residual powder image on the drum surfaceand simultaneously applies additional illumination for dischargingresidual charges thereon prior to being cleaned. The drum surface thenpasses through a cleaning station 66 at which the surface is brushed bycleaning brushes 67, rotated by a motor 68, whereby residual developingmaterial remaining on the drum is removed. Suitable light traps areprovided in the system to prevent any light rays from reaching the drurnsurface, other than the projected image, during the period of drumtravel immediately prior to sensitization by corona generating device 30until after the drum surface is completely passed through the developingstation 35.

Referring now specifically to FIGS. 2, 3, and 4 in which like referencenumerals refer to the same parts there is shown a self-cleaning coronagenerating device 30 constructed in accordance with a first embodimentof the invention. The device comprises conducting shield or housingpreferably made of aluminum or stainless steel. Shield 100 is ofgenerally inverted U-shaped cross-section and includes a top wall 101and side walls 102 in perpendicular relation to the top wall. Side walls102 terminate in converging portions 103, each arranged at an angle ofapproximately 45 to its side wall 102 and spaced apart to afford acorona discharge opening or outlet 104 at the bottom approximatelyone-half inch in width.

A corona emitting wire 105 made from any suitable noncorrosive material,such as stainless steel or platinum is stretched between and attached toblocks 106 and 107 of suitable insulating material. Wire 105 has auniform exterior and a diameter of approximately three and one-halfthousandths of an inch. Advantageously wire 105 is located approximatelyseven-sixteenths of an inch from the top wall. It should be understoodthat this distance is typical and in no way limiting on the invention.Blocks 106 and 107 are arranged between side walls 102 at the ends ofthe shield and attached by means of suitable fastening screws 108extending through top wall 101. Attached to insulating block 107 is aconductive plate 109 to which one end of wire 105 is connected at screw110 as best shown in FIG. 3. The opposite end of wire 105 is attached toinsulating block 106 by a conductive pin 111. A conductive plate 114 issecured to the shield 100 for the purpose of grounding it in anysuitable manner.

In accordance with the invention electrode wire 105 is connected tocircuitry supplying it with a high voltage ,5 sufficient 'for theemission of corona charge onto a recipient surface and also with a smallcurrent flow at predetermined intervals for purposes of cleaning it. Tothis end wire 105 is coupled to high voltage source 31 which supplies asufficiently high voltage to emit corona charge from the wire. It hasbeen found that DC voltages ranging from 4000 to about 8000 volts workswell with the corona generating device described above.

To clean dust from wire 105 a pair of double throw switches 122 and 124are moved to contact terminals 126,127, respectively, which areconnected to secondary winding 1280f a transformer 130. The primarywinding 132 of the transformer is selectively energized for apredetermined time period as will be explained more fully hereinafter.'It should now be clear that when switches 122, 124 contact terminals134, 136, respectively, the machine is in'the corona generating mode.However, when the swicthes contact terminals 126, 127, as illustratd, apredetermined current is passed through wire 105 causing the temperatureof the wire to rise sufliciently high to boil off or vaporize dust suchas electroscopic marking particles normally depositing on the wire. Ithasbeen found that currents ranging from 0.4 to 0.9 amps for to 30seconds are sufficient to vaporize particles deposited. An optimumcleaning action occurs at .84 amps for 10 seconds for corona wiresdescribed above.

The frequency at which the wire is cleaned is controlled by logic 150which is programmed to operate in any suitable manner such as after aprescribed number of cycles or time period. Another convenient manner.

for cleaning is to have logic 150 programmed to the warm-up period inthe machine. In this manner cleaning is accomplished daily to ensure ahigh corona generating efficiency. It should be noted that logic 150provides the required power input and controls energizationv time ofprimary winding 132 as well as relays for positioning double throwswitches 122 and 124. Also it should be understood that logic 150 can beadapted to manual as well as automatic operation.

It has been found that by employing wires at the lip portions of thecorona generating housing it is possible to clean away dust or dirtdeposited on the housing in a manner similar to that described. Theembodiment illustrated in FIGS. 5', 6 is intended for this purpose. Thehousing comprises a conducting shield having top wall 171 and side walls172. Extending at an angle of about 45 from side walls 172 are one ormore wires 173l'which .define a slit opening through which charge isdeposited on the xerographic plate. By passing a current'through wires173 at the same time current is passed through wire 105 as describedabove a combined cleaning action of the corona wire and housing closelyadjacent the plate where dust and dirt are most prevalent is effected.An insulating layer 175 made of any suitable material, such as Teflon,is arranged on the interior of walls 171, 172 for the purpose ofsuppressing upwardly directed corona emissions from wire 105 and furtherto insulate the housing from wires 173. It should be noted that wires173 are supported at their extremities by suitable insulating blocks notshown.

The embodiment of FIG. 6 utilizes a filament-type transformer as isknown by those skilled in the art. With this type transformer thewindings are heavily insulated making it possible to couple high voltagesource 31 directly to corotron wire 105. In this case, transformer 130has two secondary windings 180, 181 for cleaning corona wire 105 andhousing wires 173, respectively. It should be noted that wires 173,which form the lip portions of the corona generating housing, areelectrically in parallel so that if they should touch no arcing occurssince they are all at the same potential along their longitudinalextent.

By the above description, there has been disclosed a novel coronagenerating apparatus having a high current efliciency by virtue of itscapability of operating insen- .6 sitively to dust accumulation byelectr'oscopic particles as has occurred heretofore. With the cleaningarrangement described above, the unit has been found to disseminate agreatly increased ion flow to the xerographic surface charged for anindefinite period. Moreover, be cause of the inherent ability toconsistently maintain high efiiciency, the unit is capable of beingoperated closer to the corona threshold. Furthermore in one embodimentcurrent is selectively flowed through a portion of the housing toachieve a combined cleaning action.

Since many changes can be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the drawings shall be interpreted as illustrative and notin a limiting sense.

What is claimed is:

1. Self-cleaning apparatus for applying a unipolar charge uniformly ontoa chargeable member comprising a frame,

a pair of electrically non-conductive members secured to said frame inspaced apart relation along the longitudinal extent thereof,

a corona discharge electrode extending generally lengthwise between saidnon-conductive members,

a terminal at which is connected a source of high potential suflicientto emit a corona discharge from said electrode when coupled thereto,

circuit means for connecting said terminal across said electrode andincluding current generating means actuable in response to a discretesignal, and

control means for emitting a signal to said current generating means atpredetermined intervals to flow a current through said electrode for atime period sufficient to raise the temperature of said electrode to alevel to vaporize substantially all particles deposited thereon.

2. Apparatus according to claim 1 wherein said circuit means includeswitching means movable from a first position in which said electrode isoperative to emit corona charge to a second position in which saidcurrent generating means is operative to flow current through saidelectrode.

3. Apparatus according to claim 1 wherein said frame comprises a topwall and side walls, at least one resistance wire coextensive with eachside wall and positioned inwardly at an angle thereto to define a narrowopening through which corona charge may be emitted, said resistancewires being coupled to said circuit means to receive the current fromthe current generating means in common with said electrode wherebyparticles deposited on said wires are vaporized simultaneously with theaforementioned particles deposited on said electrode.

4. Apparatus according to claim 3 wherein an electrically non-conductivelayer overlies the interior surface of said walls.

5. Apparatus according to claim 1 wherein said current ranges from about.4 to about .9 amps for a time period of about 10 to about 3-0 seconds.

6. In a xerographic apparatus including a Xerographic drum comprising aphotoconductive layer on a conductive substrate, and drive means tocontinuously rotate said drum sequentially past a plurality ofprocessing stations including a charging station and a developmentstation at which electroscopic marking particles are applied to a latentelectrostatic image on said photoconductive layer, corona generatingapparatus for applying electrostatic charge uniformly onto the surfaceof said drum comprising in combination a frame,

a pair of electrically non-conductive members secured to said frame inspaced apart relation along the longitudinal extent thereof,

a corona discharge electrode extending generally lengthwise between saidnon-conductive members,

7 8 a terminal at which is connected at source of high References Citedpotential sufiicient to emit a corona discharge from i UNITED STATESPATENTS said electrode when coupled thereto, circuit means forconnecting said terminal across said a??? 25 electrode and includingcurrent generating means 5 2965756 12/1960 s g actuable in response to adiscrete signal, and 3038993 6/1962 Masuda g control means for emittinga signal to said current 3:122:634 2/1964 King generating means atpredetermined intervals to flow a current through said electrode for atime period WILLIAM R LINDQUIST, p i Examiner sufficient to raise thetemperature of said electrode 10 to a level to vaporize substantiallyall electroscopic US. Cl. X.R.

marking particles depositing thereon. 7 3553

